>> the good thing is that nasa and other agencies have been diligent about tracking this asteroid for some time now, so they have very good data on what the orbital pass of this is, and they can tell within a very few hundred feet or so, maybe a few hundred miles, how close this is to earth, and they know for sure that it won't come any closer than 17,150. that's pretty good. it's great they do that because they can look at other potentials like this too. >> we can be that accurate about its size and its pass of the earth, but let's get to this $200 billion number about what its cost would be worth. how do we get to that number? how do we put a price tag on this asteroid? >> well, you know, we could look at the composition ofas resides and figure out what their value is according to their mineral worth. if we could actually mine them and, of course, that's another story altogether, but when we think about the kind of minerals that we find there, some of them very rare ones that we need here on earth or that we use quite extentively here on earth, and we have somewhat limited supplies